1. Field of the Invention
The present invention relates to an electronic endoscope system for imaging information about a blood vessel, a processor unit for an electronic endoscope, and a method for obtaining blood vessel information.
2. Description Related to the Prior Art
In a medical field, diagnosis and treatment with use of an electronic endoscope is widely carried out in recent years. The electronic endoscope is provided with a slender insert section to be introduced into a human body cavity. The insert section contains an image sensor such as a CCD at a distal end. The electronic endoscope is connected to a light source unit. Light from the light source unit is guided through the electronic endoscope, and is emitted from the distal end of the insert section to light the inside of the body cavity. While the inside of the body cavity is irradiated with the light, the image sensor captures an image of an internal body part to be examined. The captured image is subjected to various types of processing in a processor unit connected to the electronic endoscope, and then is displayed on a monitor. The electronic endoscope can image the inside of the human body cavity in real time, and facilitates the precise diagnosis and the effective treatment.
In the light source unit, a white light source such as a xenon lamp is used to emit white light (normal light), that is, broad band light having wavelengths from the blue region to the red region. The image captured under the white light shows the whole picture of the internal body part, but cannot clearly show arrangements of shallow and deep blood vessels in the interior wall, pit patterns, and irregularities in surface tissue such as a depression or lump. At clarifying such structural details, it is known that application of narrow band light (special light) having wavelengths within a specific band is effective. It is also known that the image captured under the narrow band light provides various types of information about living tissue, e.g. an oxygen saturation level in the blood vessel.
In the endoscope system according to U.S. Patent Application Publication No. 2003/0176768, for example, the image is captured whenever light of each of three primary colors of R, G, and B is applied as the narrow band light. The longer the wavelength, the deeper point the light reaches in the interior wall. Thus, the shallow or superficial blood vessel is enhanced in the image captured under the B light. The middle blood vessel is enhanced in the image captured under the G light, and the deep blood vessel is enhanced in the image captured under the R light. Also, image data of each color is subjected to color image processing, in order to produce an image in which the shallow, middle, and deep blood vessels are distinguished by different colors.
In this endoscope system, the wavelength bands of the light of each color are sharply restricted so that the bands of the light do not overlap one another. Furthermore, after the images are captured, image signals are subjected to image processing and spatial frequency filtering processing in consideration of a hemoglobin index. This allows isolation of image data at a shallow depth i.e. near the surface of the living tissue, and prevents mixing of an image of the deep blood vessel with an image of the shallow and middle blood vessels.
In Japanese Patent No. 2648494, special light IR1, IR2, and IR3 having wavelengths in the near-infrared region is used as the narrow band light. The absorbance of the special light IR1 or IR3 by the blood vessel depends on the oxygen saturation level, while the absorbance of the special light IR2 by the blood vessel does not depend thereon. The special light IR1, IR2, and IR3 is separately applied to capture three types of special images. Then, difference in brightness is calculated among the images, and the calculated brightness difference is reflected in the image in monochrome or artificial color. This image shows information about the oxygen saturation level in the blood vessel.
In the endoscopic diagnosis, it is desirable to take advantage of not only the image having the enhanced blood vessels but also the numerical blood vessel information including the hemoglobin index and the oxygen saturation level obtained from the image, for the purpose of improving diagnostic accuracy.
However, the U.S. Patent Application Publication No. 2003/0176768 does not describe determination of the hemoglobin index and the oxygen saturation level of the blood vessel, though describes the depth of the blood vessel. The Japanese Patent No. 2648494 describes determination of the oxygen saturation level, but the oxygen saturation level is calculated without consideration of the depth of the blood vessel. Therefore, the determined oxygen saturation level could be incorrect depending on the depth of the blood vessel.